Example: FFI Table Provider as dynamic module loading

Cargo.toml

@@ -47,6 +47,9 @@ members = [
     "datafusion/substrait",
     "datafusion/wasmtest",
     "datafusion-examples",
+    "datafusion-examples/examples/ffi/ffi_example_table_provider",
+    "datafusion-examples/examples/ffi/ffi_module_interface",
+    "datafusion-examples/examples/ffi/ffi_module_loader",
     "test-utils",
     "benchmarks",
 ]

datafusion-examples/examples/ffi/README.md

@@ -0,0 +1,48 @@
+<!---
+  Licensed to the Apache Software Foundation (ASF) under one
+  or more contributor license agreements.  See the NOTICE file
+  distributed with this work for additional information
+  regarding copyright ownership.  The ASF licenses this file
+  to you under the Apache License, Version 2.0 (the
+  "License"); you may not use this file except in compliance
+  with the License.  You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+  Unless required by applicable law or agreed to in writing,
+  software distributed under the License is distributed on an
+  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+  KIND, either express or implied.  See the License for the
+  specific language governing permissions and limitations
+  under the License.
+-->
+
+# Example FFI Usage
+
+The purpose of these crates is to provide an example of how one can use the
+DataFusion Foreign Function Interface (FFI). See [API Docs] for detailed
+usage.
+
+This example is broken into three crates.
+
+- `ffi_module_interface` is a common library to be shared by both the module
+  to be loaded and the program that will load it. It defines how the module
+  is to be structured.
+- `ffi_example_table_provider` creates a library to exposes the module.
+- `ffi_module_loader` is an example program that loads the module, gets data
+  from it, and displays this data to the user.
+
+## Building and running
+
+In order for the program to run successfully, the module to be loaded must be
+built first. This example expects both the module and the program to be
+built using the same build mode (debug or release).
+
+```shell
+cd ffi_example_table_provider
+cargo build
+cd ../ffi_module_loader
+cargo run
+```
+
+[api docs]: http://docs.rs/datafusion-ffi/latest

datafusion-examples/examples/ffi/ffi_example_table_provider/Cargo.toml

@@ -0,0 +1,35 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+[package]
+name = "ffi_example_table_provider"
+version = "0.1.0"
+edition = "2021"
+publish = false
+
+[dependencies]
+abi_stable = "0.11.3"
+arrow = { workspace = true }
+arrow-array = { workspace = true }
+arrow-schema = { workspace = true }
+datafusion = { workspace = true }
+datafusion-ffi = { workspace = true }
+ffi_module_interface = { path = "../ffi_module_interface" }
+
+[lib]
+name = "ffi_example_table_provider"
+crate-type = ["cdylib", 'rlib']

datafusion-examples/examples/ffi/ffi_example_table_provider/src/lib.rs

@@ -0,0 +1,66 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+use std::sync::Arc;
+
+use abi_stable::{export_root_module, prefix_type::PrefixTypeTrait};
+use arrow_array::RecordBatch;
+use datafusion::{
+    arrow::datatypes::{DataType, Field, Schema},
+    common::record_batch,
+    datasource::MemTable,
+};
+use datafusion_ffi::table_provider::FFI_TableProvider;
+use ffi_module_interface::{TableProviderModule, TableProviderModuleRef};
+
+fn create_record_batch(start_value: i32, num_values: usize) -> RecordBatch {
+    let end_value = start_value + num_values as i32;
+    let a_vals: Vec<i32> = (start_value..end_value).collect();
+    let b_vals: Vec<f64> = a_vals.iter().map(|v| *v as f64).collect();
+
+    record_batch!(("a", Int32, a_vals), ("b", Float64, b_vals)).unwrap()
+}
+
+/// Here we only wish to create a simple table provider as an example.
+/// We create an in-memory table and convert it to it's FFI counterpart.
+extern "C" fn construct_simple_table_provider() -> FFI_TableProvider {
+    let schema = Arc::new(Schema::new(vec![
+        Field::new("a", DataType::Int32, true),
+        Field::new("b", DataType::Float64, true),
+    ]));
+
+    // It is useful to create these as multiple record batches
+    // so that we can demonstrate the FFI stream.
+    let batches = vec![
+        create_record_batch(1, 5),
+        create_record_batch(6, 1),
+        create_record_batch(7, 5),
+    ];
+
+    let table_provider = MemTable::try_new(schema, vec![batches]).unwrap();
+
+    FFI_TableProvider::new(Arc::new(table_provider), true)
+}
+
+#[export_root_module]
+/// This defines the entry point for using the module.
+pub fn get_simple_memory_table() -> TableProviderModuleRef {
+    TableProviderModule {
+        create_table: construct_simple_table_provider,
+    }
+    .leak_into_prefix()
+}

datafusion-examples/examples/ffi/ffi_module_interface/Cargo.toml

@@ -0,0 +1,26 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+[package]
+name = "ffi_module_interface"
+version = "0.1.0"
+edition = "2021"
+publish = false
+
+[dependencies]
+abi_stable = "0.11.3"
+datafusion-ffi = { workspace = true }

datafusion-examples/examples/ffi/ffi_module_interface/src/lib.rs

@@ -0,0 +1,49 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+use abi_stable::{
+    declare_root_module_statics,
+    library::{LibraryError, RootModule},
+    package_version_strings,
+    sabi_types::VersionStrings,
+    StableAbi,
+};
+use datafusion_ffi::table_provider::FFI_TableProvider;
+
+#[repr(C)]
+#[derive(StableAbi)]
+#[sabi(kind(Prefix(prefix_ref = TableProviderModuleRef)))]
+/// This struct defines the module interfaces. It is to be shared by
+/// both the module loading program and library that implements the
+/// module. It is possible to move this definition into the loading
+/// program and reference it in the modules, but this example shows
+/// how a user may wish to separate these concerns.
+pub struct TableProviderModule {
+    /// Constructs the table provider
+    pub create_table: extern "C" fn() -> FFI_TableProvider,
+}
+
+impl RootModule for TableProviderModuleRef {
+    declare_root_module_statics! {TableProviderModuleRef}
+    const BASE_NAME: &'static str = "ffi_example_table_provider";
+    const NAME: &'static str = "ffi_example_table_provider";
+    const VERSION_STRINGS: VersionStrings = package_version_strings!();
+
+    fn initialization(self) -> Result<Self, LibraryError> {
+        Ok(self)
+    }
+}

datafusion-examples/examples/ffi/ffi_module_loader/Cargo.toml

@@ -0,0 +1,29 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+[package]
+name = "ffi_module_loader"
+version = "0.1.0"
+edition = "2021"
+publish = false
+
+[dependencies]
+abi_stable = "0.11.3"
+datafusion = { workspace = true }
+datafusion-ffi = { workspace = true }
+ffi_module_interface = { path = "../ffi_module_interface" }
+tokio = { workspace = true, features = ["rt-multi-thread", "parking_lot"] }

datafusion-examples/examples/ffi/ffi_module_loader/src/main.rs

@@ -0,0 +1,63 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+use std::sync::Arc;
+
+use datafusion::{
+    error::{DataFusionError, Result},
+    prelude::SessionContext,
+};
+
+use abi_stable::library::{development_utils::compute_library_path, RootModule};
+use datafusion_ffi::table_provider::ForeignTableProvider;
+use ffi_module_interface::TableProviderModuleRef;
+
+#[tokio::main]
+async fn main() -> Result<()> {
+    // Find the location of the library. This is specific to the build environment,
+    // so you will need to change the approach here based on your use case.
+    let target: &std::path::Path = "../../../../target/".as_ref();
+    let library_path = compute_library_path::<TableProviderModuleRef>(target)
+        .map_err(|e| DataFusionError::External(Box::new(e)))?;
+
+    // Load the module
+    let table_provider_module =
+        TableProviderModuleRef::load_from_directory(&library_path)
+            .map_err(|e| DataFusionError::External(Box::new(e)))?;
+
+    // By calling the code below, the table provided will be created within
+    // the module's code.
+    let ffi_table_provider =
+        table_provider_module
+            .create_table()
+            .ok_or(DataFusionError::NotImplemented(
+                "External table provider failed to implement create_table".to_string(),
+            ))?();
+
+    // In order to access the table provider within this executable, we need to
+    // turn it into a `ForeignTableProvider`.
+    let foreign_table_provider: ForeignTableProvider = (&ffi_table_provider).into();
+
+    let ctx = SessionContext::new();
+
+    // Display the data to show the full cycle works.
+    ctx.register_table("external_table", Arc::new(foreign_table_provider))?;
+    let df = ctx.table("external_table").await?;
+    df.show().await?;
+
+    Ok(())
+}